Automated identification of articles using bar codes in the availability of the integrated circuit technology and computing power at reasonable costs. Such codes are typically used to track and identify consumer goods and other articles of manufacture. One of the first scanners capable of reading a bar code was installed at a supermarket in 1974, and by 1980 more than 90% of all grocery items carried a bar code by 1980. By December 1985, more than 12,000 grocery stores were equipped with scanner checkout systems [See, e.g., Harmon et al. (1989) Reading Between the Lines-An Introduction to Bar Code Technology, Helmers Publishing, Inc. 1989]. Bar codes have also been used in other applications, including other inventory control systems and for identification and characterization of responses to mass advertising efforts.
By electro-optically scanning the symbol on an item and generating a corresponding signal, it is possible in an associated computer whose memory has digitally stored therein the full range of items, to compare the signal derived from the scanned symbol with the stored information. When a match is found, the identity of the item and associated information, such as, in the instance of consumer goods, its price. Thus computer technology is exploited to facilitate identification procedures using machine-readable identifiers.
Bar codes are typically read using lasers that scan from left to right, right to left, or in both directions (or other directions) across a field of alternating dark bars and reflective spaces of varying widths. Multiple scans are typically employed to minimize data errors. Because of the multiplicity of bars and spaces required for each alphanumeric character, bar codes generally require a relatively large space to convey a small amount of data. For instance, each character in the bar code system known as Code 39 requires five bars and four spaces. A high density Code 39 field corresponds to only 9.4 characters per inch. Universal Product Codes (UPCs) are another common bar code used primarily in the retail grocery trade and contain a relatively large number of bars and spaces which allow for error checking, parity checking and reduction of errors caused by manual scanning of articles in grocery stores. They accordingly require even larger space for conveyance of character information. The Codabar code, which has been developed by Pitney Bowes and is used in retail price labeling systems and by Federal Express, is a self-checking code. Each character is represented by a stand-alone group of four bars and three interleaving spaces. Federal Express uses an eleven digit Codabar symbol on each airbill to process more than 450,000 packages per night. Other codes use varying bar and space techniques to represent characters. Because of error checking requirements and for other reasons, however, the space required to place a bar code on an article is relatively large.
In addition to the large surface area required for the series of bars and spaces that form a typical bar code symbol, the code must be placed on a background that has a high reflectance level. The high level of contrast, or reflectivity ratio, between the dark bars and the reflective spaces, allows the optical sensor in the reader to discern clearly and dependably the transitions between the bars and spaces in the symbol. Ideally, the printed bar should be observed as perfectly black and the spaces should be perfectly reflective. Because those ideal conditions are seldom possible, the industry typically requires that labeling media reflect at least 70% of incident light energy. Surface reflectivity and thus quality of the media on which the bar code is placed directly affects the successful use of the bar code on that media. Additionally, the media cannot be overly transparent or translucent, since those characteristics can attenuate reflected light. Accordingly, only limited types of highly reflective media may be used for placement of bar codes. Space requirements for bar codes further include a "quiet zone" that surrounds the field of bars and spaces. In many codes, this quiet zone constitutes a border around the code symbol, thus requiring even more space for the bar code.
Bar coding also requires very precise print methods. Assuming that the printing operation is capable of printing the required density to achieve the 70% reflectance ratio, careful attention must be paid to additional major factors that influence the bar code effectiveness. Those include ink spread/shrinkage; ink voids/specks; ink smearing; non-uniformity of ink; bar/space width tolerances; edge roughness and similar factors that must be closely controlled to ensure that the symbol will be easily scannable. In other words, the printer must pay careful attention to using paper or other media that displays the correct absorption properties properly inking the ribbon; carefully controlling hammer pressure; keeping the printhead and paper clean; properly wetting the paper and curing the ink; and maintaining proper adjustment of the printhead control mechanism. These printing details create additional problems and expenses, particularly for placement of bar code symbols on smaller items such as coupons and mail pieces.
"Bar codes" containing an array of marks of any desired size and shape that are arranged in a reference context or frame of one or more columns and one or more rows, together with a reference marker and a reference cue have also been developed [see, U.S. Pat. No. 5,128,528]. The number of rows corresponds to the number of characters contained in the symbology selected for the array. For example, an array that is capable of conveying all the letters of the English language and ten numeral symbols could use 36 rows. The number of columns in the matrix could corresponds to the number of characters desired to be conveyed. The roles of the rows and columns in the reference frame may be reversed if desired. In the preferred embodiment, each column contains one or more dots corresponding to the character which is desired to be conveyed in that column. The reference marker and reference cue may be formed of one shape, of two marks, or according to any other desired arrangement that allows interpretation of the matrix at any desired attitude with respect to the imaging equipment. The reference cue may form a part of the reference marker, or an information dot, if desired.
Thus, there are numerous types of bar codes, codes and methodologies for use available. Bar coding and other coding technology, however, remains to be fully exploited in areas outside the consumer products domain.